Effects of selenium on fatty acid concentration and antioxidant status of erythrocyte membrane in lambs fed linseed or sun fl ower oil diet

The effects of selenium and fatty acid supplementation on fatty acid composition and antioxidant status of erythrocyte membrane in lambs were investigated. Thirty two lambs with average body weight of 26±1 kg were divided into 4 groups and each was fed basal diet+5% linseed oil (LO), or LO+2 mg Se/ kg DM (as sodium selenite) (LOSe), or basal diet+5% sunflower oil (SO), or SO+2 mg Se/kg DM (SOSe). Selenium supplementation increased the concentration of C18:2t-10,c-12, and also the concentration of C20:5n-3 of erythrocyte membrane of the lambs fed the sunflower oil diet. Lambs fed the linseed oil diet had higher concentrations of C18:2t-10,c-12, C18:3n-3, and C20:5n-3 in erythrocyte membrane. Erythrocyte membrane of the lambs fed sunflower oil diet had higher concentrations of C18:1t-11, C18:2n-6, C18:2c-9,t-11 and C22:6n-3. Antioxidant status increased with selenium supplementation, and lambs fed sunflower oil diet had higher total antioxidative capability.


INTRODUCTION
Many studies have been investigated to increase the content of polyunsaturated fatty acids (PUFA) in lamb tissues by feeding diets supplemented with rumen protected or unprotected oilseed or free oil rich in n-6 or n-3 PUFA.However, diets rich in PUFA lead to higher susceptibility to peroxidation than diets rich in saturated fatty acids.Thus, investigations are needed to combine antioxidants with PUFA in lactating and meat producing ruminants.Selenium (Se) has been shown to affect the fatty acid (FA) composition in mouse muscle and chicken eggs (Czauderna et al., 2004a;Pappas et al., 2005).Information regarding effects of Se on FA composition in sheep is rare (Czauderna et al., 2004b,c), and there were no data published previously about the interaction of PUFA and Se on FA concentration and antioxidant status of erythrocyte membrane.Therefore the objective of the present study was to assess the effects of Se and FA supplementation on FA composition and antioxidant status of erythrocyte membrane in lambs.

MATERIAL AND METHODS
Thirty-two wether lambs (Chinese Poll Dorset×Small Tailed Han×Charolais) with average body weight of 26±1 kg divided into four groups and kept in pens individually with free access to water.The experiment was a 2×2 factorial (two Se levels and two PUFA sources) design.The experimental rations contained either linseed or sunflower oil.The linseed oil diet contained basal diet+5% linseed oil (LO) and LO+2 mg Se/ kg DM (as sodium selenite) (LOSe).Similarly, the sunflower oil diet contained basal diet+5% sunflower oil (SO) and SO+2 mg Se/kg DM (SOSe).Lambs were fed ad libitum with adjustments made on a weekly basis to minimize the amount of orts.Basal feed ingredients and nutrient content were shown in Table 1.The experiment lasted 50 days.Blood samples from each lamb were obtained by venipuncture from the jugular prior to the morning meal on the last day of the experiment, and then transferred to the tube containing EDTA (1.5 mg/ml blood).Erythrocyte membrane was prepared according to the method of Stolze and Nohl (1999).For the FA analysis, the method of Zhang et al. (2006) was used.The total antioxidative capability (TAOC) was measured by the FRAP assay (Benzie and Strain, 1996).The activity of glutathione peroxidase (GSH-Px), and the concentration of malondialdehyde (MDA) were measured according to the methods of Noguchi et al. (1973) and Mak (1983), respectively.All data were analysed as a 2×2 factorial randomized block design using ANOVA procedure of SAS.When the interaction was signifi cant, pairwise t-test was used to separate means by Se within oil source (P<0.05).
Selenium is a part of the active center of GSH-Px, which catalyzes the reduction of peroxides.MDA is a meta-stable end product of lipid peroxidation.In present study the selenium supplementation increased (P<0.01) the activity of GSH-Px and TAOC, and decreased (P<0.001) the concentration of MDA in erythrocyte membrane (Table 3).Erythrocyte membrane of lambs fed sunflower oil diet had higher (P<0.001)concentration of TAOC and lower (P<0.001)concentration of MDA than those fed linseed oil diet, which indicated the higher degree of unsaturation of n-3 PUFA than n-6 PUFA.

Table 1 .
The ingredients and chemical composition of the basal diet, DM basis

Table 2 .
Effect of diets on lamb erythrocyte membrane FA composition, g/100 g total fatty acids

Table 3 .
Effect of diets on the antioxidant status of erythrocyte membrane